The present invention is directed to a device for separating a batch of sheets from a pile of sheets and then introducing the batch into a conveyor of a machine which is designated for processing the sheets.
For an easy understanding of the process known in the prior art, reference is made to FIG. 1, wherein an uppermost group of sheets of a pile P are separated as a batch E by means of a separator S, which will engage a rear edge of the group of sheets forming the batch E. The pile P is held in place on a front surface, which is a surface facing the transfer direction G for the batch E, as the batch, such as E', is carried away by a conveyor T, by a fixed lower stop Bi and a rotatable or tiltable stop Bs. After each transfer of the batch E from the pile onto the conveyor T, the pile P is raised by means of a pile elevator R so as to maintain the uppermost sheet of the pile at a constant level, which level of the uppermost sheet, above an upper edge x of the lower fixed stop Bi, determines the height of the batch E which will be subsequently removed. In order to separate the batch E from the pile P, the separator S is moved into engagement with a rear edge of the sheets and then moved upward to raise the batch so as to form a free space M between a lowermost sheet F" of the batch E and the uppermost sheet F' of the pile. With the raising of the sheets, a pressing member N is inserted to engage the sheet F' as a pusher H engages the rear edge of the batch E and will transfer the batch onto the belts forming the conveyor T as the pivotable stop Bs is moved from a blocking position, illustrated in bold lines, to a retracted position, shown in chain lines. In order to cause the movement of the stop, a belt arrangement C is provided and in order to hold the separator S against the rear side of the sheets forming the batch E, a piston or cylinder arrangement V is provided. This type of device is disclosed in U.S. Pat. No. 4,457,658, whose disclosure is incorporated herein by reference thereto and which claims priority from a Swiss Patent Application which issued as Swiss Patent A 639045.
This process, which is generally known, has the drawback that in the event the front edge of the lowermost sheet F" of the batch E is not released from the fixed lower stop Bi after the upward tilting or lifting of the movable stop Bs and the batch E is pushed by the pusher H toward the conveyor system T, the sheet F" will either bend upward, in which case it will impair the batch evenness which is a required item for subsequent conveyance, or will bend downward, in which case it will provide very strong resistance to the advance movement of the pusher H, which resistance is likely to seriously hamper the operation of the machine in addition to causing the destruction of this particular sheet.
FIG. 1 is an illustration of the difficulty involved with choosing a contact point y for the separator S touching the rear of the pile P, which point should correspond exactly to a point x which is the level up to which the lower front stop Bi will prevent the sheets of the pile from being moved forward. In fact, on account of deformation of the sheets, especially those lying on top of the pile P, the height of the pile will only very seldom be even throughout its entire width or cross section. Since the separator S does not take this unevenness into account, this unevenness is likely to become a cause of serious troubles. This means that the separator S might separate the rear edge of the sheet F", whose front edge is not engaged with the upper edge x of the lower stop Bi, in which case the sheet F" can be shifted by the pusher H toward the conveyor system T. However, the separator can also separate the rear edge of a sheet F", whose front edge is still engaged with an upper edge x of the lower stop Bi, in which case, as commented above, the lower sheet cannot be easily removed from the pile by the pusher H and will cause problems.